Automatic gage control and method of operating for rolling mill



Oct. 22, 1968 H. A. LIST 3,406,547

AUTOMATIC GAGE CONTROL AND METHOD OF OPERATING FOR ROLLING MILL Filed Aug. 2, 1966 United States Patent 3,406,547 AUTOMATIC GAGE CONTROL AND METHOD OF OPERATING FOR ROLLING MILL Harold A. List, Bethlehem, Pa., assignor to Bethlehem Steel Corporation, a corporation of Delaware Filed Aug. 2, 1966, Ser. No. 569,745 Claims. (Cl. 72-8) This invention relates to rolling mills and more particularly to an automatic gage control system for rolling mills.

In the past so-called gagemeter gage control systems such as basically disclosed in Patent 2,680,978 to Hessenberg et al. have been used in combination with X-ray or similar radiation type gage determining devices to automatically control the rolling of strip in rolling mills. In such mills the X-ray' gage determines long term changes such as mill heating and strip cooling and corrects overall errors in the gage of the strip rolled by the use of the gagemeter system. Other rolling mills have used the X- ray gage as the primary control system for the adjustment of mill screw downs to produce strip of a desired gage. In either case the unavailability of the X-ray signal due to malfunction, or, in more modern systems, traversing of a traversing type X-ray gage to determine camber of the strip, has left such previous mills without the effective control provided by the X-ray gage so that such mills must be temporarily operated without this control signal, or manually operated, or even completely shut down, if the loss of the signal is of long duration. A recent development has been the increasing use of two adjacent X-ray gages with the expectation that at least one will be operating at all times. X-ray gages are delicate devices, however, and particularly in hot strip mills are exposed to very unfavorable environmental conditions. Furthermore, X-ray gages are expensive to duplicate, and, even if one of a pair is operating, if the other is of the traversing type, and is actually traversing to determine the camber of the strip, its gage control signal will usually be u'navailable for overall control of the gage of strip passing through the mill.

It is an object of this invention therefore to provide a rolling mill control system and method of operating the same which does not require an operating X-ray gage for effective continuous control of strip gage. It is a further object of the present invention to provide superior compensation for long range changes in a mill control system.

I have discovered that the above objects can be attained by providing a roll force signal from a succeeding mill stand to control the stand normally at least partially controlled by the X-ray gage which roll force signal will substitute for the X-ray signal when this is unavailable, or provide improved compensation of the system when it is available.

In the drawing there is shown a diagrammatic illustration of a portion of a rolling mill incorporating the control system of the present invention.

In the drawing is shown the exit end of a hot strip rolling mill 11 including a last rolling stand 13, a second last rolling stand 15, a third last rolling stand 17, and the rolls only of a rolling stand 19, the remaining parts of which are not shown, preceding stand 17. It will be understood that still other rolling stands, not shown, may precede stand 19.

Each stand has a pair of work rolls 21 and 23 rotatably journaled in suitable bearing blocks 25 and 27. Backup rolls 29 and 31 are rotatably journaled in bearing blocks 33 and 35. Upper bearing blocks 25 and 33 are mounted for vertical movement in each respective stand under the influence of mill screws 37 which are movably threaded 3,406,547 Patented Oct. 22, 1968 in the usual mill nuts, not shown, in housings 39 and splined in gears 41 meshing with worm gears 43 driven by screwdown motors 45. Screwdown motors 45 are operated from screwdown controllers 47 of any suitable type. Mill screws 37 and associated mechanism on each mill provide a strip gage regulating mechanism. Controllers 47 determine the screwdown positions and roll openings in the mills initially provided by set point means 49 which may be set by manual or computer means. On mill stands 13 and 15, respectively, load cells 51 and 53 are positioned under lower bearing blocks 35 in a recess in windows 55 of the housings 39. Although only one load cell is visible in each housing 39 of stands 13 and 15 in the drawing, it will be understood that an identical load cell is also positioned under the bearing block at the opposite ends of backup rolls 31 in mill stands 13 and 15 and that the load cell signal from each is fed to summing amplifiers 57 or 59 for mill stand 13 or 15 respectively where the signals are summed and amplified to provide a signal, the magnitude of which indicates the force between the work rolls 21 and 23 of each respective mill.

A traversing X-ray gage 61 is located after stand 13. An X-ray or radioactive ray source is contained in lower head 63 supported by movable U-bracket 65 which is mounted upon rollers, not shown, on a track 67 on supports 69. An X-ray detector is contained in upper head 71 supported on the upper portion of movable U-bracket 65. U-bracket 65 may be traversed, or moved transversely of strip 73 along track 67 by means of traversing motor 75, the operation of which is controlled by position controller 77. Ordinarily position controller 77 will position heads 71 and 63 centrally of strip 73 in order to measure the overall gage of strip 73. When it is desired to determine the camber of the strip, or the gage of the strip near the edges, position control 77 will be activated by the mill operator or alternatively by suitable timing mechanism to operate traversing motor and move heads 71 and 63 adjacent the near edge of strip 73 as shown in dotted outline in the drawing or adjacent the far edge of the strip as may be appropriate.

The summed load cell signal from load cell 53 and the matching load cell on the far side of mill stand 15 is directed from summing amplifier 59 to an algebraic computer 79 which also receives a reference signal from a signal device such as potentiometer 81 which may be adjusted manually or preset by punched card apparatus or the like and develops a voltage proportional to the desired screw setting or opening between work rolls 21 and 23 of mill stand 15. Algebraic computer 79 also receives a screw position signal from selsyn 83 which position sig nal is derived from the position of gear mechanically connected to selsyn 83 by a suitable drive 84 which gear detects the rotational position of gear 41 of mill screw 37. As is conventional in gagemeter systems algebraic computer 79 determines the additional opening between work rolls 21 and 23 due to the yield of the mill from the magnitude of the load cell signals and adds this to the screw position signal received from selsyn 83, or other suitable screw position detection apparatus, to determine the approximate actual opening between the work rolls, and compares this with the reference signal from potentiometer 81 which indicates the desired signal. The difference between the summed load cell and screw position signals and the reference signal is then directed as an error signal to screwdown control 47A which operates screwdown motor 45A to remove the error in the opening between the rolls.

An initial set point signal is received by screwdown controller 47A from set point 49 to initially set the mill screwdowns before strip enters the mill or between strips.

Screwdown controller 47A also receives an integrated strip gage signal from X-ray gage 61, which signal is algebraically summed with the error signal from computer 79 in screwdown controller 47A to aid in positioning the screwdown of mill stand 15. The signal from the X-ray detector in head 71 of X-ray gage 61 is compared in algebraic computer 87 with a voltage signal derived from a reference signal device such as potentiometer 89 on which the desired X-ray Signal indicative of the desired gage of the strip is preset. The difference between the reference signal and the X-ray signal, or, in other words, the error signal, is then directed by algebraic computer 87 through contact 91 to integrating computer 93 where the error signal is integrated and then directed to screwdown controller 47A. The integrated X-ray error signal provides an adjustment of screwdowns 37 of mill stand through screwdown controller 47A which compensates for errors in the gage of strip 73 caused by long range factors such as progressive heating of the mill stands and cooling of the strip. The integration of the signal provided by integrating computer 93 allows a correction signal to be held to maintain the correct strip gage after a long term correction is made.

A second X-ray error signal is directed by algebraic computer 87 through contact 95 to screwdown controller 478 of mill stand 13. This X-ray error signal will operate screwdown motor 45B via controller 47B to adjust the screwdown of mill stand 13 approximately according to the integral of the X-ray error signal received from algebraic computer 87 to make a final correction in the gage of the strip issuing from the mill. It may be ad-vantageous in some instances if the X-ray error signal to screwdown control 47B is integrated separately as described elsewhere for stand 15, particularly when, as explained hereinafter as an alternative embodiment, the load cell error signal from rolling stand 13 is used to modify the gagemeter signal on rolling stand 15 in combination with the X-ray error signal,

The load cell signal from load cell 51 is summed with the load cell signal from an identical load cell, not shown, under the bottom bearing block on the far side of mill stand 13, by summing amplifier 57 and the summed signal is directed to comparator 97 wher it is compared with a voltage signal from a reference signal device such as potentiometer 99 which is adjusted by a reversing motor 101, the operation of which is controlled by servoamplifier 103. The difference between the load cell signal and the reference signal is directed from comparator 97 as an error signal via line 105, tap 107, and contacts 109 and 111, to servoamplifier 103 which is so constructed that it drives reversing motor 101 in a direction to adjust potentiometer 99 to match the load cell signal from summing amplifier 57 and so provide a zero error signal from comparator 97 to servoamplifier 103.

Line 105 from comparator 97 also leads via normally open contact 113, or, alternatively, via tap 115 and normally open contact 117, to integrating computer 119 which directs an integrated signal to screwdown controller 47A which signal, when received, will activate controller 47A to make a further correction of the screwdown position through screwdown motor A in addition to that initiated by the gagemeter error signal from algebraic computer 79, and, in case contact 117 is closed, from the integrated X-ray error signal from integrating computer 93.

Preferably integrating computer 119 should be a resetting integrator which resets itself each time the load cell signal is completely removed from it due to the opening of contacts 113 or 17. A line 120 may also be provided through contact 122 from summing amplifier 57 to integrating computer 119 to reset the integration cycle every time load cell 51 detects a new strip in mill stand 13 after a previous strip has left the mill. Opening of contact 122 will prevent resetting of the integration cycle between strips if continuing operation is desired.

Contacts 95, 91, 109 and 113 are all carried upon shaft 121 of a solenoid 123. For convenience of illustration solenoid coil 125 of solenoid 123 is shown in series with the output of position controller 77 to traversing motor of X-ray gage 61 so that solenoid coil 125 will be activated to operate solenoid 123 at any time traversing motor 75 is activated to traverse X-ray gage 61. It will be obvious that other more sophisticated control arrangements may be contrived to operate solenoid 123 when X-ray 61 is in traversing position, or other than its central position, regardless of whether traversing motor 75 is activated or not,

When solenoid coil 125 is activated normally closed contacts 95, 91 and 109 are opened, and normally open contact 113 is closed. The opening of contacts 91 and 95 removes the X-ray error signal from screwdown controllers 47A and 47B, respectively, while X-ray gage 61 is traversing. The gagemeter signal from algebraic computer 79 will continue to control screwdown controller 47A to adjust the roll opening of stand 15. However, since there is no gagemeter control on mill stand 13, and this stand is controlled, after the initial setting of the mill through set point 49, entirely by the X-ray error signal received from algebraic computer 87, the screwdown of stand 13 will not be further adjusted while X- ray gage 61 is traversing, This is normally not greatly detrimental as the X-ray error signal provided to screwdown controller 478 is not normally adjusted to make large or fast screwdown corrections.

As explained previously, while contact 109 is closed the load cell error signal from comparator 97 is directed through contact 109 to servoamplifier 103 which continuously adjusts potentiometer 99 through reversing motor 101 so that the reference signal matches the load cell signal and the load cell error signal from comparator 97 is continuously brought to zero. When contact 109 is opened as a result of the activation of solenoid 123 when the X-ray gage 61 is traversing the error signal is no longer supplied to servoamplifier 103 and the error signal is consequently no longer brought to zero by adjustment of potentiometer 99, which potentiometer remains at its last adjusted position. At the same time normally open contact 113 is closed by the action of solenoid 123 and the load cell error signal from comparator 97 is directed through contact 113 to integrating computer 119 where the signal is integrated and then directed to screwdown controller 47A to modify the control provided by the gagemeter signal at stand 15.

As the strip becomes cooler, and consequently harder, it will be reduced less in stand 13 and load cell 51 will detect a progressively greater load in the mill stand. The resultant increasing load cell signal is compared with the now constant reference signal from potentiometer 99 and the resulting load cell error signal after being integrated in integrating computer 119 modifies the adjustment of the screwdown of mill stand 15 through screwdown controller 47B to compensate for long term variations in strip gage caused by cooling of the strip, which are not taken care of by the gagemeter on mill 15, and which are usually compensated for by the error signal derived from X-ray gage 61. It will be understood that any factor which causes the strip passing into stand 13 from stand 15 to either increase or decrease in gage will increase or decrease the load in stand 13 and the load cell signal from stand 13. This load cell signal after being integrated may be used as a long term correction signal in place of the long term integrated correction signal ordinarily derived from the X-nay gage.

When X-ray gage 61 has completed its traversing cycle, or is otherwise stopped, position control 77 will position it centrally of the strip by the operation of traversing motor 75 and will then deactivate motor 77, at the same time deactivating solenoid 123 to close contacts 95, 91 and 109 and open contact 113 returning the system to its previous condition.

If the X-ray gage signal from gage 61 should become unavailable due to failure of the X-ray gage rather than due to traversing of the gage 61, the load cell error signal can be substituted for the X-ray error signal by first opening contact 111 manually or otherwise to remove the feedback of the load cell signal to servoamplifier 103 and then closing contact 117 manually or otherwise to apply the load cell error signal to screwdown controller 47A after integration in integrating computer 119.

in some cases it may be beneficial to operate screwdown controller 47A with both the integrated X-ray signal and the integrated load cell signal from the following mill stand applied as control signals to it at the same time as lOng term corrections to the gagemeter error signals on the mill. This may be done by closing contact 117 and opening contact 111. In this instance the gain of summing amplifier 57 will normally be adjusted low during normal operation and turned up if the X-ray gage signal becomes unavailable and the load cell signal must substitute completely for the X-ray signal. Once the load error signal is properly calibrated it is a more reliable signal and has certain stability advantages over the X-ray signal used alone in making long term corrections.

As an alternate system in a hot strip mill, if integrating computer 119 is designed to be reset every time a signal is received in it from summing amplifier 57 via line 120 and contact 122 indicating a new strip is entered in mill stand 13, both the X-ray and load cell integrated signals may be used to control screwdown controller 47A in addition to the gagemeter signal from algebraic computer 79. The integrated load cell error signal, the integration of which is restarted at the beginning of each new strip, will then compensate for temperature rundown on each strip due to progressive cooling of the strip, and the integrated X-ray error signal which is not reset at the beginning of each new strip will compensate for the progressive heating of the mill itself during a continuous run as more and more hot strips are rolled in the mill. 'In this case contact 117 may be held open at the beginning of rolling of each strip either manually or automatically by suitable control circuits, not shown, until the error signal from algebraic computer 87 indicates that strip is being produced within a desired range. Alternatively contact 117 may be held open at the beginning of rolling of each strip until servoamplifier 103 has had suflicient time to balance the load cell error signal to zero, at which time contact 111 may be opened to hold reference potentiometer 99 at a constant setting and contact 117 closed to begin a load cell control cycle. Contact 111 may be opened by means of a solenoid, not shown, energized by a timer, also not shown, activated by a signal derived from load cell 51. Since resetting of integrating computer 119 at the end of each strip in a sense returns the load cell signal to zero, regardless of the reference setting, in many applications it will not be necessary to reset the reference signal for each strip but the setting can be left the same during any continuous run of the mill.

1f mill stand 15 in the drawing did not incorporate a gagemeter arrangement but were controlled exclusively during the passage of a strip through the rolls by a direct X-ray gage error signal in the same manner that mill stand 13 is controlled, as illustrated in the drawing without an X-ray error signal integrating means, the load cell signal from stand 13 could still be substituted for the primary X-ray signal when the X-ray signal is unavailable due either to traversing or to failure.

The X-ray signal is desirable in the first instance as a control signal as it is a more directly calibrated gage signal. Thus while the substitution of a succeeding load cell error signal derived from a following mill for a normal X-ray signal has been found particularly useful where the X-ray signal functions primarily to compensate for temperature rundown and similar elfects, it will be recognized that the substitution will be useful wherever an X-ray signal is used to control the gage of strip in a rolling mill stand, either through control of the screwdowns or through control of some other strip gage regulating mechanism such as means to control the tension of the strip. It will also be recognized that although the invention is illustrated with reference to the last two stands of a hot rolling mill it would also be applicable to any mill stand in a hot or cold rolling mill at least partially controlled by an X-ray gage and having a succeeding mill stand located thereafter in the rolling mill which mill stand can be held with a constant or nearly constant roll opening, at least during the time the load cell signal is substituted for the X-ray signal.

I claim:

1. A method of operating a rolling mill wherein strip gage regulating mechanism is controlled at least partially by a gage signal from a succeeding radiation type gage which measures the gage of the strip in the mill comprising:

(a) controlling the adjustment of said strip gage regulating mechanism at least partially from a strip gage indicating radiation type signal,

(b) interrupting said strip .gage indicating radiation signal, and

(c) substituting therefor during said interruption a load cell signal from a rolling mill stand of said rolling mill succeeding said strip gage regulating mechanism to control said mechanism to regulate the gage of the strip during said interruption while the radiation signal is unavailable for control purposes.

2. The method of operating a rolling mill according to claim 1 wherein the load cell signal is integrated before being used to adjust said strip gage regulating mechamsm.

3. The method of operating a rolling mill according to claim 1 wherein the radiation type gage is in addition a traversing radiation type gage comprising:

(d) controlling the strip gage adjustment mechanism from the radiation signal of the traversing radiation gage while said gage is measuring the gage of a central portion of the strip leaving a rolling stand of said rolling mill,

(e) interrupting said radiation signal controlling the strip gage regulating mechanism when the traversing radiation gage moves to either side of the central portion of the strip,

(f) substituting the load cell signal for said radiation signal during said interruption to control the strip gage regulating mechanism, and

(g) resubstituting the X-ray signal for control of said regulating mechanism when said radiation gage returns to measuring the central portion of the strip.

4. The method of operating a rolling mill according to claim 3 wherein the load cell signal is integrated before being used to adjust said strip gage regulation mechanism.

5. A control system for continuous regulation of strip gage in a rolling mill comprising:

(a) a control circuit to control the operation of a strip gage regulating mechanism on the mill in response to an externally received gage control signal indicative of the gage of the strip passing said regulating mechanism,

(b) a traversing radiation gage to provide a strip gage indicating control signal to said control circuit,

(c) a load cell located on a mill stand succeeding said gage regulating mechanism to provide a strip gage indicating control signal to the control circuit, and

(d) switching control means operative to remove the radiation gage signal from the control circuit when the radiation gage traverses from the central portion of the strip and substitute therefor the said load cell signal.

6. A control system for a rolling mill according to claim 5 additionally comprising a reference signal control circuit for continuously adjusting said load cell signal to zero by means of an adjustable reference signal while the radiation signal is switched into said control circuit for said strip gage regulating mechanism and for holding said reference signal at a substantially constant value when said load cell signal is switched into said control circuit for said strip regulating mechanism.

7. A control system for a rolling mill according to claim in which said load cell signal is integrated before being used as a control signal.

8. A control system for a rolling mill including a first rolling stand preceding a second rolling stand comprising:

(a) load cell means to provide a first signal proportional to the separating force between, the rolls of the first rolling stand,

(b) load cell means to provide a second signal proportional to the separating force between the rolls of the second rolling stand,

(0) means to provide a third signal proportional to the separation between the rolls of the first stand,

(d) reference signal means to indicate the desired separation between the rolls of the first rolling stand by a fourth signal,

(e) reference signal means to indicate the desired separating force between the rolls of the second rolling stand by a fifth signal,

(f) means to convert said first signal into a sixth signal proportional to the increased separation between the rolls of said first rolling stand due to the yield of the mill under said separating force,

(g) means to combine said third and said sixth signals and balance the combined signal against said fourth signal to provide a roll position control signal,

(h) means to compare said second and fifth signals to provide a roll force error signal, and

8 (i) means to combine said roll force error signal algebraically with said position control signal in a predetermined ratio to provide a corrected control signal for controlling strip gage regulating mechanism associated with said first rolling stand.

9. A control system for a rolling mill according to claim 8 in which the roll force error signal is integrated by an integrating means before being combined with said position control signal in order to provide compensation for long term effects such as temperature rundown.

10. A control system for a rolling mill according to claim 9 in which said integrating means is adapted to be reset after the passage of each strip through said second rolling stand and an integrated error signal from a radiation gage is combined as a control signal with said roll force error signal and said position control signal in order to provide compensation for long term effects such as mill heating.

References Cited UNITED STATES PATENTS 2,339,359 1/1944 Shayne et a1. 7212 2,959,992 Ill 1960 Mitchell 72234 3,006,225 10/1961 Mamas 72234 3,186,200 6/1965 Maxwell 72234 3,355,918 12/1967 Wallace 7216 3,357,217 12/ 1967 Wallace 728 CHARLES W. LANHAM, Primary Examiner.

A. RUDERMAN, Assistant Examiner. 

1. A METHOD OF OPERATING A ROLLING MILL WHEREIN STRIP GAGE REGULATING MECHANISM IS CONTROLLED AT LEAST PARTIALLY BY A GAGE SIGNAL FROM A SUCCEEDING RADIATION TYPE GAGE WHICH MEASURES THE GAGE OF THE STRIP IN THE MILL COMPRISING: (A) CONTROLLING THE ADJUSTMENT OF SAID STRIP GAGE REGULATING MECHANISM AT LEAST PARTIALLY FROM A STRIP GAGE INDICATING RADIATION TYPE SIGNAL, (B) INTERRUPTING SAID STRIP GAGE INDICATING RADIATION SIGNAL, AND (C) SUBSTITUTING THEREFOR DURING SAID INTERRUPTION A LOAD CELL SIGNAL FROM A ROLLING MILL STAND OF SAID ROLLING MILL SUCCEEDING SAID STRIP GAGE REGULATING MECHANISM TO CONTROL SAID MECHANISM TO REGULATE THE GAGE OF THE STRIP DURING SAID INTERRUPTION WHILE THE RADIATION SIGNAL IS UNAVAILABLE FOR CONTROL PURPOSES.
 5. A CONTROL SYSTEM FOR CONTINUOUS REGULATION OF STRIP GAGE IN A ROLLING MILL COMPRISING: (A) A CONTROL CIRCUIT TO CONTROL THE OPERATION OF A STRIP GAGE REGULATING MECHANISM ON THE MILL IN RESPONSE TO AN EXTERNALLY RECEIVED GAGE CONTROL SIGNAL INDICATIVE TO THE AGREE OF THE STRIP PASSING SAID REGULATING MECHANISM, (B) A TRAVERSING RADIATION GAGE TO PROVIDE A STRIP GAGE INDICATING CONTROL SIGNAL TO SAID CONTROL CIRCUIT, (C) A LOAD CELL LOCATED ON A MILL STAND SUCCEEDING SAID GAGE REGULATING MECHANISM TO PROVIDE A STRIP GAGE INDICATING CONTROL SIGNAL TO THE CONTROL CIRCUIT, AND (D) SWITCHING CONTROL MEANS OPERATIVE TO REMOVE THE RADIATION GAGE SIGNAL FROM THE CONTROL CIRCUIT WHEN THE RADIATION GAGE TRANSVERSES FROM THE CENTRAL PORTION OF THE STRIP AND SUBSTITUTE THEREFOR THE SAID LOAD CELL SIGNAL. 